The process water at 80°F is pumped at a rate of 800-1,500 USGPM and is heated by a two-stage system with three burners in a series. A portion of the water is removed after the first burner at 120°F and the remainder of the flow is heated to 170°F. The exhaust gases from all three burners are pumped through the cold incoming water in a preheating stage of the heat recovery unit. This arrangement results in a low stack temperature of 105°F and the resulting overall system efficiency is calculated at 96.5% as compared to 75% boiler efficiency.
Monticello Wastewater Treatment Plant
Environmental legislation passed by the US Congress a few years ago has resulted in increased pressure on US wastewater treatment facilities to address the problem of environmental discharge of potentially harmful pathogens in treated municipal liquid waste.This means that all new wastewater treatment facilities or modernization projects have to look for new ways of producing Class A biosolids.
A 2 MM BTU/hr system operating with digester biogas and alternately natural gas was installed in 1998 to provide this function for the Monticello wastewater treatment plant in Monticello, Minnesota.Cold activated sludge at a continuous flow of 65 USGPM enters the system at 50°F and passes through a spiral sludge-to-sludge heat exchanger with an outlet temperature of 120°F. The sludge enters the heating unit, where it is heated to 158°F and passed to the internal flow-through tank retention
compartment.Sludge leaves the tank through the other side of the spiral heat exchanger and to the anaerobic digesters at a final temperature of 100°F.The products of combustion are collected by a biofilter odor control system, making this installation the first closed-loop submerged combustion system. This system not only preheats the sludge — eliminating the need for boiler heating of the digesters — but also contributes both evaporated moisture and heat from the products of combustion to the biofilter, which would otherwise also have to be heated by a boiler. The closed-loop nature of the process gives this installation an overall thermal efficiency of 100%.
Konica Manufacturing Plant
A 10 MM BTU/hr, dual fuel (natural gas and #2 heating oil) system was installed in April 2002 to provide water heating for Konica’s photographic paper manufacturing process in Whitsett, North Carolina.This two-stage system,which displaces an 80% efficient steam boiler,heats 1,100 USGPM of water to 120- 140°F with a 125°F stack temperature and an overall efficiency of 94.5%.
Future Uses
A change in emphasis by industrial users from simple fuel/cost savings to GHG emissions reduction and environmental compliance puts submerged combustion in the forefront of “green” technologies in the field of combustion. New applications for submerged combustion technology currently being investigated include LNG evaporators; electrolyte heaters for copper electrowinning processes; evaporators for produced water reduction from oil wells; evaporators for production of concentrated acids; heating systems for iron ore slurries; and large scale, multistage process water heating applications for tar sands projects.
Conclusion
As burner technology progresses, emissions of NOx, CO and VOCs by industry will be reduced and eventually eliminated. Emissions of CO2,however,are related not to burner efficiency but to appliance efficiency. As long as low efficiency heating methods involving boilers are used for industrial processes, their associated CO2 emissions and stack temperatures will not be reduced to any significant degree. Alternative heating methods such as submerged combustion, with its higher efficiencies, lower CO2 emissions and lower stack temperatures, offer an engineering benefit that helps to best utilize our energy reserves in a responsible manner.
Steven Panz PEng is Director of Energy Systems for Inproheat Industries Ltd,a 45 year old BC based company.Mr Panz has carried out project engineering on a variety of steam and power related industries throughout Western Canada.
Eric Panz Ing (Austria),President of Inproheat Industries, founded the company in 1958.He has worked in thermal process,heat and combustion technologies for over 40 years.
Joseph Jachniak PEng, who is Chief Engineer and Head of Research and Development for Inproheat Industries, is responsible for project development, execution and management as well as process engineering and system startups.
